JPH0781633B2 - Automatic transmission for hydraulically driven vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic transmission for a hydraulically driven vehicle having a hydraulic transmission.

[Conventional technology]

Hydraulic transmissions in hydraulically driven vehicles such as tractors and graders have a variable displacement hydraulic pump (swash plate pump) driven by the engine on the engine side and a variable displacement hydraulic pump on the drive shaft side that drives the wheels or tracks of the vehicle. A motor (swash plate motor) is provided, which transfers the driving force of the engine to the wheels or crawler belts by guiding the hydraulic oil discharged from the swash plate pump to the swash plate motor through hydraulic piping. By controlling the inclination angle of the swash plate of the hydraulic motor, the discharge amount of the hydraulic pump and the suction amount of the hydraulic motor per one revolution of the engine are adjusted to shift gears.

Such an automatic transmission for a hydraulically driven vehicle forms an automatic shift signal based on the difference between the set engine speed set by the throttle lever and the actual engine speed, and uses this signal to perform the above-mentioned speed change. It was output as one of the signals.

[Problems to be solved by the invention]

The automatic shift signal has a slow response to a load change,
Especially for shovel-type tractors that require quick gear shifting, there is a drawback that sufficient vehicle performance cannot be obtained.

That is, the mechanism of automatic shifting will be described with reference to the control block diagram shown in FIG. 2. The load 5 becomes heavy.

 The rotation of the hydraulic motor 4 decreases.

The suction oil amount Q _M of the hydraulic motor 4 decreases.

The pressure P of the hydraulic pipe 3 increases (the discharge amount Q _P of the hydraulic pump 2 is constant).

The load torque of the engine 1 (the input shaft torque τ _P of the hydraulic pump 2) increases.

The engine speed N _{E of the} engine 1 decreases.

 The output current I of the control circuit 6 decreases.

The output of the servo device 7 (pump tilt angle θ _P ) becomes small.

 Engine load torque decreases.

 The rotation speed of the engine 1 increases.

Therefore, with respect to the change of the pump input shaft torque τ _P , there is an inertia term of the engine 1 until the engine speed N _E decreases, and a shift is delayed.

[Means for solving problems]

Therefore, in the present invention, the fluctuation of the load is detected from the pressure of the hydraulic pipe of the hydraulic transmission, and the detected pressure is also used as a parameter for forming the automatic shift signal.

[Action]

Since the pressure change in the hydraulic pipe due to the load change is faster than the change in the engine rotation, the speed can be changed quickly by using the pressure as a parameter for forming the automatic shift signal.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of a drive system to which an automatic transmission system for a hydraulically driven vehicle according to the present invention is applied. In the figure, a hydraulic transmission 10 is provided with a variable displacement hydraulic pump (hereinafter simply referred to as hydraulic pump) 11 and a variable displacement hydraulic motor (hereinafter simply referred to as hydraulic motor) 12, which are connected by hydraulic pipes 13a and 13b. The shaft 11a of the hydraulic pump 11 is connected to the output shaft 1a of the engine 1 and is rotationally driven by the engine 1. The shaft 12a of the hydraulic motor 12 is connected to drive wheels of a vehicle (not shown), and drives the drive wheels to rotate.

Generally, the variable displacement type of the hydraulic pump is suitable for the application of constant output shaft torque, and the variable displacement type of the hydraulic motor is suitable for the constant output.In this embodiment, both the hydraulic pump 11 and the hydraulic motor 12 are variable. The capacity type is used to combine the features of both. The hydraulic pump 11 and the hydraulic motor 12 are both variable displacement pumps and variable displacement motors that change the displacement volume by changing the inclination angles of the swash plates 11b and 12b.

The pump swash plate servo device 14 controls the discharge direction and discharge amount of the hydraulic oil of the hydraulic pump 11, and the swash plate according to the polarity and magnitude of the pump capacity change signal S _P from the control device 20.
Controls the tilt direction and tilt angle of 11b. The hydraulic pump 11 discharges the hydraulic oil in the direction and flow rate according to the inclination direction and the inclination angle of the swash plate 11b. The inclination direction of the swash plate 11b of the hydraulic pump 11 is controlled so that the hydraulic oil is discharged to the hydraulic pipe 13a side when moving forward and discharged to the hydraulic pipe 13b side when moving backward. The motor swash plate servo device 15 is for controlling the suction amount of the hydraulic oil of the hydraulic motor 12, and the swash plate 12b of the hydraulic motor 12 is responsive to the motor capacity change signal Sm from the control device 20.
It is designed to control the tilt angle of. The rotation direction and the torque of the hydraulic motor 12 change according to the direction and the inflow amount (suction amount) of the inflowing hydraulic oil. Therefore, the shift control of the transmission 10 can be performed by controlling the discharge amount of the hydraulic pump 11 and the suction amount of the hydraulic motor 12.

The control circuit 20 is a vehicle speed setting lever for setting the vehicle speed.
Potentiometer 2 for generating signals corresponding to 21 positions
4, potentiometer 25 for generating a signal corresponding to the position of brake pedal 22, potentiometer 27 for generating a signal corresponding to the position of throttle lever 23, and engine 1
The various signals of the engine rotation sensor 26 for generating a pulse signal corresponding to the number of revolutions are input, and the signals are respectively arranged in the hydraulic pipes 13a and 13b of the hydraulic transmission 10 to generate a signal corresponding to the internal hydraulic pressure thereof. inputs the signal from the oil pressure sensor 28 and 29, performs a computation to be described later, from these signals, generates the pump displacement changes the signal S _P and the motor capacity control signal Sm controls the capacity of the hydraulic pump 11 and hydraulic motor 12.

Next, the control circuit 20 will be described with reference to the block diagram shown in FIG. The control circuit 20 includes a vehicle speed control arithmetic circuit 30 to which signals are applied from potentiometers 24 and 25, an engine rotation sensor 26, a potentiometer 27, and a hydraulic pressure sensor 28.
And an automatic shift calculation circuit 40 to which signals are added from 29 and 29,
It is composed of a servo drive circuit 50 and the like.

The vehicle speed control calculation circuit 30 includes an absolute value circuit 31 and a forward / backward movement determination circuit.
32, adders 33 and 34, etc., and a signal R ₄ for suppressing the maximum value of an automatic shift signal V ₂ described later in response to the operation of the vehicle speed setting lever 21 and the brake pedal 22.
And a forward / reverse switching signal K _FR .

The potentiometer 24 applies a signal R ₁ corresponding to the operating position of the vehicle speed setting lever 21 to the absolute value circuit 31 and the forward / backward movement determination circuit 32. The signal R ₁ is lever 21 is a voltage S, and the voltage -S next time maximum speed position of the reverse, the voltage O when the neutral position signal when the maximum speed position forward.

The absolute value circuit 31 takes the absolute value of the input signal R ₁ and outputs the signal R ₂
To the negative input of adder 33. The voltage S is applied to the positive input of the adder 33, and the adder 33 adds the two inputs and adds the signal R ₃ (= S−R ₂ ) to the positive input of the adder 34. Adder
A signal B corresponding to the depression amount of the brake pedal 22 (this signal B is, for example, a signal that changes from voltage O to S in proportion to the depression amount) is added to the other positive input of 34 from the potentiometer 25, and the addition is performed. The device 34 adds the two input signals and outputs a suppression signal R ₄ (= R ₃ + B).

The suppression signal R ₄ becomes O when the brake pedal 22 is not operated and the lever position of the vehicle speed setting lever 21 is the maximum forward / reverse speed position, and S when it is in the neutral position.

The forward / reverse discriminating circuit 32 discriminates the polarity of the input signal R ₁ and outputs a forward / reverse switching signal K _FR which is “1” when positive and “−1” when negative.

On the other hand, the automatic shift calculation circuit 40 includes a frequency-voltage converter 41,
It consists of adders 42 and 43, clamper 44, PID compensation circuit 45, and selection circuit 60.
26, the potentiometer 27, the hydraulic pressure sensors 28 and 29, and the shift signal V ₂ are formed based on the signals from the forward / backward movement determination circuit 32.

The engine rotation sensor 26 applies a pulse signal having a pulse number corresponding to the rotation speed of the engine 1 to the frequency-voltage converter 41,
The frequency-voltage converter 41 converts the input pulse signal into a voltage signal V _NE corresponding to the number of pulses and _applies it to the positive input of the adder 42. The signal V _NE is a signal having a voltage of 11.5 S when the engine speed is 2300 rpm, for example.

The potentiometer 27 outputs a signal V _TH corresponding to the operation position of the throttle lever 23. For example, when the lever 23 is in a position to command the engine speed 2100 rpm, the signal V _TH becomes a signal of voltage 10.5S. This signal V _TH is added to adder 4
Added to 2 negative inputs. Further, S is added to the other positive input of the adder 42, and the adder 42 adds these three inputs and adds the addition result to the positive input of the adder 43.

Oil pressure sensors 28 and 29 generate signals V _P1 and V _P1 corresponding to the internal oil pressures of hydraulic pipes 13a and 13b, respectively. The signals V _P1 and V _P2 are, for example, signals proportional to the oil pressure, and are signals that become the voltage S when the oil pressure is 500 kg / cm ³ . These signals V _P1 and V _P2 are applied to the selection circuit 60.

The selection circuit 60 selects the signal on the high-pressure side of the signals V _P1 and V _P2 , and only when that selected signal indicates the hydraulic pressure of the hydraulic pipe on the discharge side of the hydraulic pump 11, the signal is set as the signal V _P. FIG. 4 shows a detailed circuit of the output.

In FIG. 4, the selection circuit 60 is composed of a high voltage side selection circuit 70 and a judgment circuit 80.

The high voltage side selection circuit 70 further includes a changeover switch 71, a comparator 72, and a relay 73. The signal V _P1 from the oil pressure sensor 28 is applied to the contact 71a of the changeover switch 71 and the comparator 72, and the oil pressure sensor 2
The signal V _P2 from 9 is the contact 71b of the selector switch 71, the comparator 72
Other inputs have been added.

The comparator 72 compares the two input signals and outputs a signal “1” when V _P1 ≧ V _P2 and outputs a signal “0” when V _P1 <V _P2 . The relay 73 is energized when the signal “1” is applied from the comparator 72, connects the movable contact piece 71c of the changeover switch 71 to the contact point 71a,
When the signal "0" is applied, the signal is turned off and the movable contact piece 71c of the changeover switch 71 is connected to the contact point 71b. Therefore, the high pressure side selection circuit 70 always outputs a signal corresponding to the pressure of the high pressure side hydraulic pipe.

The determination circuit 80 includes an exclusive NOR circuit 81, a relay 82, and a switch 83. Only when the input signal is a signal indicating the pressure of the hydraulic pipe on the discharge side of the hydraulic pump 11, the switch 83 is turned on and the signal is set as the signal V _P. It is what is output.

That is, the exclusive NOR circuit 81 is added with the output from the comparator 72 and the forward / reverse switching signal K _FR from the forward / backward determination circuit 32, and the exclusive NOR circuit 81 receives the negative OR of the two input signals. Takes logic, that is, signal K _FR is "1" (forward)
When the output of the comparator 72 is "1" (V _P1 on the high voltage side) and when the signal K _FR is "-1" (reverse), the output of the comparator 72 is "0" (V _P2 on the high voltage side). Only when this occurs, the signal "1" is output to the relay 82 and the relay 82 is energized. When the relay 82 is energized, it turns on the switch 83, and outputs the high voltage side signal input to the switch 83 as the signal V _P.

The determination circuit 80 determines whether the signal on the high voltage side is generated when the vehicle is moving forward or backward in response to an increase in load, or when the vehicle brakes during deceleration and downhill. As described above, the high voltage side signal is output only in the former case.

The signal V _P selected as described above is added to the negative input of the adder 43 of the automatic shift calculation circuit 40 (FIG. 3). The adder 43 adds this signal and the signal from the adder 42 added to the positive input, and outputs the signals V ₁ and V ₁ = S + V _NE −V _TH −V _P ………… (1) to the clamper 44. Output.

The clamper 44 limits the signal to S when the input signal V ₁ is S or more and to O when it is O or less, and outputs this signal as an automatic shift signal V ₂ via the PID compensation circuit 45. The PID compensation circuit 45 is provided to prevent the engine rotation and vehicle speed from becoming unstable during automatic gear shifting.

This automatic shift signal V ₂ is applied to the positive input of the adder 51.
The suppression signal from the vehicle speed control arithmetic circuit 30 is applied to the negative input of the adder 51.
R ₄ is added, and the adder 51 adds the two inputs and outputs the signal.
V ₃ a (= V ₂ -R ₄₎ is output as a final transmission signal.

The servo drive circuit 50 controls the discharge direction and discharge amount of the hydraulic pump 11 of the transmission 10 and the suction amount of the hydraulic motor 12, and the pump is controlled so as to have a gear ratio corresponding to the shift signal V ₃ added from the adder 51. and outputs a capacitance change signal S _P and the motor capacity change signal Sm. Further, the servo drive circuit 50 determines the polarity of the pump capacity change signal S _P according to the polarity of the forward / reverse switching signal K _FR . Pump capacity change signal
S _P is added to the coils 52a and 52b of the solenoid valve 52 that operates the pump swash plate servo device 14, and the motor capacity change signal Sm is the coil of the solenoid valve 53 that operates the motor swash plate servo device 15.
Added to 53a.

Therefore, the pump swash plate servo device 14 and the motor swash plate servo device 15 control the inclination angle of the swash plate according to the signals S _P and Sm, and control the discharge amount of the hydraulic pump 11 and the suction amount of the hydraulic motor 12. Shift control of the transmission 10 is performed.

Next, the operation of the automatic shift calculation circuit 40 will be described. Now, assuming a dozer shovel as a hydraulically driven vehicle, give a command that the engine speed becomes 2100 rpm with the throttle lever 23, run from an unloaded stop state, thrust the bucket of the dozer shovel into the ground, and put sand into the bucket. A case where the vehicle is driven by driving will be described.

In this case, the signals V _P , V _TH , V _NE , V ₁ and V ₂ in each of the above states are as shown in the following table.

In Table 1, V ₁ is a value calculated based on the equation (1), and V ₂ is an output (automatic shift signal) of the clamper 44 of the calculated value. FIG. 5 shows the relationship between the actual engine speed and the hydraulic pressure on the high pressure side in the above case.

As is clear from FIG. 5, the rise of the hydraulic pressure during a sudden load is faster than the fall of the engine speed, and therefore the start point of the downshift operation (the change point of the automatic shift signal V ₂ ) is faster. . By the way, the engine stalls when the gear is not changed within 0.5 seconds under load, but in the case of the present invention, it is about 0.1 second faster than the change time of the conventional automatic speed change signal due to the decrease in the engine speed, and is responsive to the load change. Will get better.

As described above, in the determination circuit 80 of the selection circuit 60, the traveling state in which the hydraulic pressure is high because the engine 1 is reversely driven as in the case of a downhill (that is, the load is increased because the engine braking is effective). The high-pressure side hydraulic signal Vp is selected and output only when it is determined that the vehicle is in the loaded traveling state excluding the running state in which the vehicle is running.

As a result, the automatic shift signal V3 is obtained in which the start time of downshift becomes faster as the pressure increases based on the hydraulic pressure signal Vp, only in the load running state except the load running state in which the engine braking is in effect. , Automatic shift is started immediately before the change in engine speed.

As described above, according to the embodiment, the hydraulic signal Vp does not affect the automatic shift when the engine is braking and the vehicle is in the load traveling state, and the normal automatic shift in which Vp is zero in the above equation (1) is performed. Is done.

Here, depending on the vehicle, when the vehicle is descending a slope or decelerating, the engine has no load or a reverse load, and the operator may freely change gears. Occurs, and especially in the case of a shovel-type dozer, the load may be spilled, which is not preferable. Therefore, during such a downhill or decelerating traveling state, a normal automatic shift that is not an abrupt shift is performed, so body swing during engine braking is avoided, and it is possible to prevent the occurrence of spillage of cargo, etc. .

Further, in the load traveling state in which the engine brake is not effective, quick automatic gear shifting is performed by the hydraulic signal Vp.

Here, when a large load is suddenly applied to the engine to excavate the earth and sand, it is desired to shift down as quickly as possible to increase the traction force. Therefore, in the load traveling state such as during the excavation work, the rapid automatic shift is performed, so that the excavation work can be efficiently performed due to the increase in the traction force.

The method of forming the automatic shift signal is not limited to this embodiment, and in short, when the automatic shift signal is formed, the engine set speed is changed to the shift signal based on the actual speed, and the component due to the hydraulic pressure of the transmission is added to Any element may be added as long as the pressure is higher so that a decelerating signal is obtained.

〔The invention's effect〕

As described above, according to the present invention, when the engine is in the reverse drive state, the automatic shift similar to the conventional one is performed. That is, an automatic shift signal is generated based on the deviation between the set engine speed set by the engine speed setting means and the actual engine speed.
A final gear shift signal is generated based on a signal indicating a gear ratio that is externally set (for example, set by a vehicle speed setting lever or a brake pedal), and a hydraulic pump of a hydraulic transmission is generated according to the gear shift signal. And the displacement volume of at least one of the hydraulic motors is changed to perform automatic gear shifting. In this way, the normal automatic shift is performed, so that careless rocking of the vehicle body is suppressed.

However, when the engine is not reversely driven, the hydraulic pressure signal on the high pressure side of the two hydraulic pipes is used to shift down when the pressure is increasing and when the pressure is decreasing. An automatic shift signal for upshifting is generated. Therefore, compared to the case of normal automatic shifting,
It is possible to prevent the engine from excessively decreasing its revolution speed, etc. by performing a quick gear change.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a drive system to which an automatic transmission system for a hydraulically driven vehicle according to the present invention is applied, and FIG. 2 is a block diagram used to explain conventional problems, and FIG. FIG. 4 is a block diagram showing an embodiment of a control circuit according to the present invention, FIG. 4 is a circuit diagram showing details of the selection circuit of FIG. 3, and FIG. 5 is engine speed and hydraulic pressure of transmission hydraulic oil due to load fluctuation. It is a figure which shows the transient response of. 1 ... Engine, 10 ... Hydraulic transmission, 11
...... Variable displacement hydraulic pump, 12 ... Variable displacement hydraulic motor,
14 …… Pump swash plate servo device, 15 …… Motor swash plate servo device, 20 …… Control circuit, 21 …… Vehicle speed setting lever, 22 ……
Brake pedal, 23 ...... Throttle lever, 24,25,27 ...
… Potentiometer, 26 …… Engine rotation sensor, 28,2
9 ... Oil pressure sensor, 30 ... Vehicle speed control calculation circuit, 31 ... Absolute value circuit, 32 ... Forward / backward movement determination circuit, 40 ... Automatic shift calculation circuit, 41 ... Frequency-voltage converter, 44 ... Clamper , 50
...... Servo drive circuit, 60 …… Selection circuit, 70 …… High voltage side selection circuit, 80 …… Judgment circuit.

Claims (1)

[Claims] 1. An automatic gear shift signal is generated based on a deviation between a set engine speed set by an engine speed setting means and an actual engine speed, and the automatic gear shift signal and a gear ratio set externally. In the automatic transmission of a hydraulically driven vehicle that changes the displacement volume of at least one of the hydraulic pump and the hydraulic motor of the hydraulic transmission based on a signal indicating that the hydraulic pump and the hydraulic motor are First and second hydraulic pressure detecting means, which are respectively arranged in two hydraulic pipes to be connected and which detect the internal hydraulic pressure thereof and output a hydraulic signal corresponding to the detected pressure, and the first and second hydraulic pressure detecting means. The high pressure side selection means for selecting the high pressure side oil pressure signal among the detected pressures and the high pressure side oil pressure detection means for outputting the high pressure side oil pressure signal selected by the high pressure side selection means. Judgment means for judging that it is arranged in the hydraulic pipe on the discharge side corresponding to the traveling direction of the driving vehicle, and the hydraulic signal on the high-pressure side only when the judgment is made by the judgment means. Based on the above, an automatic transmission device for a hydraulically driven vehicle is provided, which has means for generating an automatic shift signal that shifts down when the pressure is increasing and upshifts when the pressure is decreasing.